This invention relates to the detection of a sheared element in a mechanical structure, and, in particular, to a method and apparatus for electrical detection and reporting of a sheared element.
Mechanical equipment utilizes shearing elements or shearing pins to limit the mechanical load so that the shearing element is destroyed to prevent the application of an excessive mechanical load which would damage the equipment. Sheared elements are replaced during the repair of the equipment. Shear pins have been used in aircraft equipment to prevent damage or destruction to the equipment when mechanical loads exceed a predetermined limit.
The detection and reporting of destroyed or sheared shear pins is necessary for their replacement and the continued safe operation of the equipment. A sheared pin in a remote section of a large piece of equipment, such as an aircraft, may not be known or reported unless it is detected and reported through an electrical circuit to a data collection point. Electrical detection means have been used in the past. Such means has a wire that goes through the shear pin and is insulated from it. An excessive mechanical load limit causes the shear pin to shear which hopefully cuts the wire in two, providing an indication that the shear pin had sheared. Shear pins of this type have a disadvantage in that failure of the wire to shear cleanly may prevent the shear pin from acting as a full shear. Such wire type shear pins also have a disadvantage in that the shearing action may cause the wire to short, resulting in a failure to detect and report the sheared pin. Further, in applications where the sheared pin is constantly monitored, an open circuit may occur and the monitoring system is unable to distinguish whether the signal is the result of a sheared pin or whether the wire circuit has opened. In addition, with wire type shear pins an electrical short between the wires outside of the shear pin or an electrical short between the wires and "ground" would preclude detection of the sheared pin. Thus, there is a need for an apparatus and a method for reducing the problems with prior electrical detection of shear pins and to more accurately distinguish between a sheared element and wiring anomalies.